The present invention relates to a process for coating powder particle substrates, the coated powder particle substrates and to applications and uses thereof. More particularly, the invention relates to coating powder particle substrates with a metal non-oxide-containing material, such material preferably being an electrically and/or thermally conductive non-oxide-containing material and such coated powder substrates.
In many applications using powder it would be advantageous to have an electrically and/or thermally conductive; radiation absorbing and/or anti friction metal non-oxide coatings which are substantially uniform, have high and/or designed conductivity and/or radiation absorbing properties and have good chemical properties, e.g., morphology, stability, corrosion resistance, etc.
A number of techniques have been employed to provide certain metal non-oxide coatings on fixed generally larger size substrates. For example, the CVD processes are well known in the art for coating a single flat surface, which is maintained in a fixed position during the contacting step. The conventional CVD process is an example of a xe2x80x9cline-of-sightxe2x80x9d process or a xe2x80x9ctwo dimensionalxe2x80x9d process in which the metal non-oxide is formed only on that portion of the substrate directly in the path of the metal source as metal non-oxide is formed on the substrate. Portions of the substrate, particularly internal and external surfaces, which are shielded from the metal non-oxide being formed, e.g., such as the opposite side and edges of the substrate which extend inwardly from the external surface and substrate layers which are internal or at least partially shielded from the depositing metal non-oxide source by one or more other layers or surfaces closer to the external substrate surface being coated, do not get uniformly coated, if at all, in a xe2x80x9cline-of-sightxe2x80x9d process. Such shielded substrate portions either are not being contacted by the metal source during line-of-sight processing or are being contacted, if at all, not uniformly by the metal source during line-of-sight processing. A particular problem with xe2x80x9cline-of-sightxe2x80x9d processes is the need to maintain a fixed distance between the source and the substrate. Otherwise, metal non-oxide can be deposited or formed off the substrate and lost, with a corresponding loss in process and reagent efficiency.
There has been a need to develop processes for producing metal non-oxide coated powder substrate particles and processes, particularly under fast reaction processing conditions, which provide short processing times required for producing high quantities of metal non-oxide coated powder particle substrates and to produce unique metal non-oxide coated powder substrates having improved properties
A new process, e.g., a xe2x80x9cnon-line-of-sightxe2x80x9d or xe2x80x9cthree dimensionalxe2x80x9d process, useful for coating of three dimensional powder particle substrates has been discovered. As used herein, a xe2x80x9cnon-line-of-sightxe2x80x9d or xe2x80x9cthree dimensionalxe2x80x9d process is a process which coats surfaces of a powder substrate with a metal non-oxide coating which surfaces would not be directly exposed to metal non-oxide-forming compounds being deposited on the external surface of the substrate during the first line-of-sight contacting step. In other words, a xe2x80x9cthree dimensionalxe2x80x9d process coats coatable powder substrate surfaces which are at least partially shielded by other portions of the powder substrate which are closer to the external surface of the powder substrate and/or which are further from the metal non-oxide forming source during processing, e.g., the internal and/or opposite side surfaces of for example glass, ceramic or mineral powder particle substrates such as fibers, spheres, flakes or other shapes or surfaces including porous shapes.
A new fast reaction, elevated temperature process for coating a three dimensional powder substrate having shielded surfaces with a metal non-oxide, preferably a conductive or absorbing metal non-oxide coating on at least a part of all three dimensions thereof and on at least a part of said shielded surfaces thereof has been discovered. In brief, the process comprises forming a reaction mixture comprising powder substrate particles, a metal non-oxide precursor, for example, silicon, aluminum, boron and titanium precursors, such as partial oxide and chloride containing precursors and an anion forming precursor preferably at least the powder substrate particles and metal non-oxide precursor being in a liquid form and/or in a flowable powder form said metal and the anion of the precursor being chemically different and reacting the reactant mixture under fast reaction short residence time, high temperature reducing conditions in a reaction zone to form a metal non-oxide coated substrate and recovering such coated substrate, preferably a conductive or radiation absorbing non-oxide-containing coated substrate.
The anion forming precursor is typically a precursor agent that provides the non-oxide portion of the metal such as boron, nitrogen, silicon, carbon and sulfur. The anion forming precursors can be in the form of a gas, liquid or solid for example methane and carbon powder as a source for carbon, nitrogen and ammonia as a source for nitrogen, boron halides such as boron trichloride as a source for boron, sulfur halides and hydrogen sulfide as a source for sulfur and various silicon halides and hydrosilicides as a source for silica.
The forming of the metal non-oxide precursor/substrate and anion forming precursor reactant mixture preferably takes place closely in time to reacting in the reaction zone. In a particularly preferred embodiment, the reaction mixture after formation is introduced directly into the high temperature reaction zone under fast reaction processing reducing conditions. The coated powder substrate is then recovered by conventional means.
The process can provide unique coated substrates including single and mixed non-oxides which have application designed conductivity and/or absorbing properties and/or anti friction lubricant properties so as to be suitable for use as components such as additives in a wide variety of applications. Substantial coating uniformity, e.g., in the thickness of the metal non-oxide coating is obtained. Further, the present metal non-oxide coated substrates in general have outstanding stability, e.g., in terms of electrical or thermal properties and morphology and are thus useful in various applications.